drmModeCreateLease() should return a new lease fd for every succesful call.
Make sure that our dummy implementation does the same.
Returning 0 will cause stdout to be closed at the end of each test,
which will break the test logging when tests are run without forking
(ie. when CK_FORK=no)
Bug-AGL: SPEC-3815
Change-Id: I6b9436a962fb25b88576ae1c950c4f6f698e949a
Signed-off-by: Damian Hobson-Garcia <dhobsong@igel.co.jp>